A device for producing a partial vacuum in a motor vehicle with an internal-combustion engine already has many uses. The provision of the partial vacuum in most vehicles is necessary, in particular for the functioning of brake servo-units supplied with partial vacuum. In these, the difference between the atmospheric pressure and the partial vacuum is exploited to increase the braking force on the brake cylinder. Safe operation of the brake servo-unit and therefore the brake system of the motor vehicle therefore always requires that an adequate partial vacuum be maintained in the vacuum chamber of the brake servo-unit by means of a non-return valve to ensure adequate braking force in every driving situation. The quantity control member for the power control of the internal-combustion engine generally controls the intake air flow and therefore the power of the internal-combustion engine by means of a rotary adjustment of a throttle valve. The disadvantage in this principle in relation to the possibility of tapping off a partial vacuum is the partial vacuum in the intake manifold which is different at a different power setting of the internal-combustion engine and dependent on the driving situation. Especially in the case of vehicles with comfort equipment such as an automatic transmission and a powerful air-conditioning system, the inlet pipe partial vacuum is not sufficient, in some circumstances, in conjunction with a spark ignition engine which has been optimised with regard to the part load throttle losses, to reliably supply the brake system. Stop-and-go driving situations on a downhill slope with high ambient temperatures have to be taken into account here, in particular.
An intake air sucking jet pump is occasionally provided parallel to the throttle valve connection piece to improve the partial vacuum level. By exploiting the corresponding part of the intake air flow as a propellant, an increased partial vacuum can be produced in a Venturi tube according to Bernoulli's law as a result of the generally known principle of cross-sectional constriction and the increase in speed connected therewith.
To provide the partial vacuum, electrically or mechanically driven partial vacuum pumps have already also been proposed, which, however, have a poor overall degree of efficiency because of the multiple energy conversion in the motor vehicle with an internal-combustion engine. In addition, the partial vacuum pumps used as auxiliary units give rise to considerable parts costs and lead to a higher susceptibility to faults of the overall system. The operating liability of a pneumatic brake servo-unit is therefore adversely affected and this is an important safety risk when operating the motor vehicle.
A device for producing and/or augmenting the partial vacuum in a pneumatic brake servo-unit for the brake system of a motor vehicle driven by an internal-combustion engine by means of a sucking jet pump is proposed in DE 198 08 548 A1, in which the sucking jet pump is arranged in the exhaust system of the internal-combustion engine and is used as a propellant for the exhaust gas mass flow of the internal-combustion engine. The disadvantage in this arrangement is the position of the device in the hot exhaust gas of the internal combustion engine which severely limits the possibilities for using various thermally unstable materials. In addition, the exhaust gas mass flow is proportionally dependent on the throttle valve position and engine speed so when the throttle valve is closed and there is therefore a small charge air flow, the exhaust gas mass flow also does not produce an adequate flow in every operating situation of the motor vehicle to ensure adequate partial vacuum to operate the pneumatic brake servo-unit.
DE 195 03 568 A1 relates to a quantity-controlled internal-combustion engine with a sucking jet pump arranged in a bypass to the quantity control member or throttle valve for the partial vacuum production of a servo motor, in particular of a brake servo-unit, wherein a shut-off valve and/or throttle valve provided in the bypass upstream from the sucking jet pump is arranged. Although adequate production of a partial vacuum is possible with this structure even with a small fluid flow of the charge air, the arrangement has an external structure which is arranged next to the quantity control member acting as a throttle unit, and has further individual parts which have to be integrated in the engine compartment. In addition, a shut-off valve and/or throttle valve is required which disadvantageously has to be electrically activated.
A throttle valve connection piece for an internal combustion engine of a motor vehicle with a throttle valve which can be adjusted in a channel is proposed in DE 196 22 378 A1, in which the region of the channel with a throttle valve is bridged by a bypass channel. Viewed in the flow direction, an electrically switchable valve is firstly arranged in the bypass channel followed by a Venturi tube. A partial vacuum mechanism for a brake servo-unit is connected in the entry region of the Venturi tube. This arrangement also requires, externally to the throttle valve connection piece, a structure which has to be integrated in the engine compartment. In addition, because of the varying fluid flow in the channel, a valve is required which has to be controlled by an actuating element.
The problem occurs in these known methods that external inlet pipe arrangements are necessary that have to be integrated in the engine compartment, these, electrically or mechanically, having valves, which require electrical control and, in addition, are expensive and lead to increases susceptibility of the system to faults.
A device is known from FR 834 168 A, in which external arrangements and electrical controls are not necessary to produce a partial vacuum. The disadvantage here is, however, that an assured production of partial vacuum and in particular an improvement in partial vacuum is not possible, which is very important when operating partial vacuum brake servo-units, in particular.
It is therefore at least one object of the present invention to provide a device for producing and/or augmenting a partial vacuum in a motor vehicle by means of which for every idling or overrun operating point of the vehicle or the internal-combustion engine, the partial vacuum is improved within the laws relating to flow, so partial vacuum brake servo-units can be operated in such a way that an increased braking force assistance is available at all times. In addition, other object, desirable features and characteristics of the present invention will become apparent from the subsequent summary, detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.